With the emergence of new blood gas analyzers that are capable of measuring a large number of different parameters from a small amount of whole blood, such as for example 200 .mu.l., and the demand by the populace to cut or lower the cost of health care, in the field of arterial blood gas testing, the focus is on devices that are easy to use, yet technologically advanced. In other words, in the blood gas, electrolyte, metabolite, co-oximetry test field, the drive is toward blood collection devices that collect only a minute amount of blood and that are compatible with all the blood gas analyzers and/or co-oximeters.
Furthermore, for patients who are difficult to take blood from, for example such as neonates or older patients, there is a definite need for a reliable blood-drawing device that is designed to withdraw only a tiny amount of blood, such as for example 500 .mu.l (0.5 cc) or less.
One such proposed product is disclosed in U.S. Pat. No. 5,386,834. In particular, this device comprises a protective tube into which are mounted two concentric glass capillaries. The protective tube is open at one end whereat a tapered member is mounted. This tapered member has an opening through which one end of a first of the capillaries extends. The other end of the first capillary is held by a connecting member located at the closed end of the protective tube. The second capillary also has one of its ends attached to the connecting member, which holds the respective ends of both capillaries in position and in communication with each other. The other end of the second capillary is held in place by the mounting member and is in open communication with the interior of the protective tube. There are two ventilation bores in the protective tube.
In operation, a cannula is connected to the exposed end of the first capillary. Once the patient is punctured by the cannula, blood is collected by means of capillary action and possibly blood pressure into the first capillary, and then the second. The phlebotomist has to make sure that a sufficient amount of blood is collected in the first capillary, so that there will be a sufficient amount of blood for evaluation. Since the second capillary has an open end, blood always overflows the open end of the second capillary into the protective tube, and in an extreme condition, possibly leaks out of the ventilation holes. A scenario of such happening is, for example, when the phlebotomist fails to notice that the collected blood has reached the end of the second capillary.
In addition to the real chance that possibly contaminated blood may leak out of the protective tubing, the flow of blood into the '834 device takes some time, since the respective diameters of the capillaries are rather small and each length of the capillaries is relatively long. So, too, since the amount of required blood to be collected may differ depending on the type of test being run, the '834 device needs to have different sized capillaries, for example one for 250 .mu.l and one for 500 .mu.l. And since the capillaries, as well as the protective tube are clear, a phlebotomist may mistake the larger-sized device from the smaller one once filled. Further, since the capillaries are made of glass, they are easily breakable. Furthermore, the structure of the '834 device is such that it is adaptable only to certain types of blood gas analyzers.
There is therefore a need for an inexpensive, yet reliable blood-collecting device that is suitable for collecting an adequate yet minute amount of blood from patients who require that there be minimal trauma.